Support corner positions

[leonard-thieu]

Support for corner positions (top left, top right, bottom left, bottom right) would be useful, particularly for elements (that are positioned near corners) with large tooltips.

Consider the following screenshot as an example. Clicking on the smiley face opens up a tooltip containing a menu. The menu only manages to be partially rendered in the window. The same would apply to any of the cardinal directions. Being able to position it top left would allow it to be fully rendered on screen.

Please ignore the separate issue I'm having where all items in a tooltip that have tooltips all show their tooltips regardless of their trigger event.